Ducted fan vehicles particularly useful as VTOL aircraft

ABSTRACT

A vehicle, including a vehicle frame, a duct carried by the vehicle frame with the longitudinal axis of the duct perpendicular to the longitudinal axis of the vehicle frame, a propeller rotatably mounted within the duct about the longitudinal axis of the duct to force an ambient fluid therethrough from its inlet at the upper end of the duct through its exit at the lower end of the duct, and thereby to produce an upward lift force applied to the vehicle, and a plurality of parallel, spaced vanes pivotally mounted to and across the inlet end of the duct about pivotal axes perpendicular to the longitudinal axis of the duct and substantially parallel to the longitudinal axis of the vehicle frame, the vanes being selectively pivotal about their axes to produce a desired horizontal force component to the lift force applied to the vehicle.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to ducted fan vehicles, and particularlyto such vehicles useful as VTOL (Vertical Take-Off and Landing)aircraft.

Many different types of VTOL aircraft have been proposed where theweight of the vehicle in hover is carried directly by rotors orpropellers, with the axis of rotation perpendicular to the ground. Onewell known vehicle of this type is the conventional helicopter whichincludes a large rotor mounted above the vehicle fuselage. Other typesof vehicles rely on propellers that are installed inside circularcavities, shrouds, ducts or other types of nacelle, where the propelleror rotor is not exposed, and where the flow of air takes place insidethe circular duct. Most ducts have uniform cross-sections with the exitarea (usually at the bottom of the duct when the vehicle is hovering)being similar to that of the inlet area (at the top of the duct). Someducts, however, are slightly divergent, having an exit area that islarger than the inlet area, as this was found to increase efficiency andreduce the power required per unit of lift for a given inlet diameter.Some ducts have a wide inlet lip in order to augment the thrustobtained, especially in hover.

VTOL vehicles are usually more challenging than fixed wing aircraft interms of stability and control. The main difficulty rises from the factthat, contrary to fixed wing aircraft which accelerate on the grounduntil enough airspeed is achieved on their flight surfaces, VTOLvehicles hover with sometimes zero forward airspeed. For these vehicles,the control relies on utilizing the rotors or propellers themselves, orthe flow of air that they produce to create control forces and momentsand forces around the vehicle's center of gravity (CG).

One method, which is very common in helicopters, is to mechanicallychange, by command from the pilot, the pitch of the rotating rotorblades both collectively and cyclically, and to modify the main thrustas well as moments and/or inclination of the propeller's thrust linethat the propeller or rotor exerts on the vehicle. Some VTOL vehiclesusing ducted or other propellers that are mounted inside the vehiclealso employ this method of control. Some designers choose to change onlythe angle of all the blades using ducted or other propellers that aremounted inside the vehicle for this method of control. The angle of allthe blades may be changed simultaneously (termed collective control) toavoid the added complexity of changing the angle of each bladeindividually (termed cyclic control). On vehicles using multiple fanswhich are relatively far from the CG, different collective controlsettings can be used on each fan to produce the desired control moments.

The disadvantage of using collective controls, and especially cycliccontrols, lies in their added complexity, weight and cost. Therefore, asimple thrust unit that is also able to generate moments and sideforces, while still retaining a simple rotor not needing cyclic bladepitch angle changes, has an advantage over the more complex solution.The main problem is usually the creation of rotational moments ofsufficient magnitude required for control.

One traditional way of creating moments on ducted fans is to mount adiscrete number of vanes at or slightly below the exit section of theduct. These vanes, which are immersed in the flow exiting the duct, canbe deflected to create a side force. Since the vehicle's center ofgravity is in most cases at a distance above these vanes, the side forceon the vanes also creates a moment around the vehicle's CG.

However, one problem associated with vanes mounted at the exit of theduct in the usual arrangement as described above, is that even if theseare able to create some moment in the desired direction, they cannot doso without creating at the same time a significant side force that hasan unwanted secondary effect on the vehicle. For such vanes mountedbelow the vehicle's CG (which is the predominant case in practical VTOLvehicles), these side forces cause the vehicle to accelerate indirections which are usually counter-productive to the result desiredthrough the generation of the moments by the same vanes, therebylimiting their usefulness on such vehicles.

The Chrysler VZ-6 VTOL flying car uses vanes on the exit side of theduct, together with a small number of very large wings mounted outsideand above the duct inlet area.

However, in the VZ-6, the single wing and the discrete vanes were usedsolely for the purpose of creating a steady, constant forward propulsiveforce, and not for creating varying control moments as part of thestability and control system of the vehicle.

The Hornet unmanned vehicle developed by AD&D, also experimented withusing either a single, movable large wing mounted outside and above theinlet, or, alternatively using a small number of vanes close to theinlet side. However these were fixed in angle and could not be moved inflight.

Another case that is sometimes seen is that of vanes installed radiallyfrom the center of the duct outwards, for the purpose of creating yawingmoments (around the propeller's axis).

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

One object of the present invention is to provide a vehicle with aducted fan propulsion system which also produces rotary moments and sideforces for control purposes. Another object of the invention is toprovide a vehicle of the foregoing type particularly useful for VTOLaircraft.

According to a broad aspect of the present invention, there is provideda vehicle, comprising: a vehicle frame; a duct carried by the vehicleframe with the longitudinal axis of the duct perpendicular to thelongitudinal axis of the vehicle frame; a propeller rotatably mountedwithin the duct about the longitudinal axis of the duct to force anambient fluid therethrough from its inlet at the upper end of the ductthrough its exit at the lower end of the duct, and thereby to produce anupward lift force applied to the vehicle; and a plurality of spacedvanes pivotally mounted to and across the inlet end of the duct aboutpivotal axes perpendicular to the longitudinal axis of the duct andselectively pivotal about their axes to produce a desired horizontalcontrol force in addition to the lift force applied to the vehicle.

It has been found that such a vehicle equipped with a plurality of suchvanes pivotally mounted across the inlet of the duct (as distinguishedfrom the exit end of the duct) can indeed produce a combination of sideforces with rotational moment that is favorable to the normal control ofthe vehicle. It has also been found that such vanes across the inlet endof the duct, particularly when combined with a second plurality of vanesacross the outlet end of the duct, can produce desired forward, aft,left and right translation movements, as well as yaw, pitch and rollrotary movement of the vehicle.

In some described preferred embodiments, the vanes are substantiallyparallel to the longitudinal axis of the vehicle frame.

Another embodiment is described wherein the vanes include a first groupof parallel vanes extending across one half of the inlet of the duct andpivotal about axes at a predetermined acute angle with respect to thelongitudinal axis of the vehicle frame; and a second group of parallelvanes extending across the remaining half of the inlet end of the ductand pivotal about axes at the predetermined angle, but in the oppositedirection, with respect to the longitudinal axis of the vehicle frame;the first and second groups of vanes being selectively pivotal toproduce a desired net control force in addition to the lift forceapplied to the vehicle.

According to further features in the described preferred embodiments,the vanes have a symmetrical airfoil shape and are spaced from eachother a distance approximately equal to the chord length of the vanes.

In one described preferred embodiment, each of the vanes is pivotallymounted as a unit for its complete length to produce a desired sideforce component. In a second described embodiment, each of the vanes issplit into two halves, each half of all the vanes being separatelypivotal from the other half of all the vanes, whereby the componentforce to the lift force applied to the vehicle is a rotary moment forceabout the duct longitudinal axis.

Other embodiments are described wherein, in one case, each of the vanesis pivotally mounted about an axis passing through the vane, and inanother case, each of the vanes includes a fixed section and a pivotalsection pivotally mounted at the trailing side of the fixed section.

According to further features in some described preferred embodiments,the duct includes a second plurality of parallel, spaced vanes pivotallymounted to and across the inlet end of the duct about pivotal axesperpendicular to the pivotal axes of the first-mentioned plurality ofvanes and perpendicular to the longitudinal axis of the duct.

In one described preferred embodiment, the pivotal axes of the secondplurality of vanes are in a plane vertically spaced from the pivotalaxes of the first-mentioned plurality of vanes; whereas in a seconddescribed embodiment, the pivotal axes of the second plurality of vanesare in a common plane with that of the pivotal axes of thefirst-mentioned plurality of vanes. With respect to the latterembodiment, it may be desirable to have a slight shift in the two planesin order to offset the pivotal mounting of the vanes, but in such case,the shift would be relatively small, e.g., less than one chord length.

Another embodiment is described wherein the duct includes a secondplurality of spaced vanes pivotally mounted to and across the exit endof the duct about pivotal axes perpendicular to the longitudinal axis ofthe duct and selectively pivotal about their axes to produce anotherdesired side control force or rotary moment control force, in additionto the lift force applied to the vehicle.

Since the foregoing features of the invention are especially useful withrespect to VTOL aircraft vehicles, the invention is described belowparticularly with respect to such vehicles, but it will be appreciatedthat the invention, or various features thereof, could also beadvantageously used in other vehicles, such as sea vehicles.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 illustrates one form of VTOL aircraft vehicle constructed inaccordance with present invention;

FIG. 2 illustrates only one of the ducted fans in the aircraft of FIG.1;

FIG. 3 is a sectional view along line III--III of FIG. 2;

FIG. 4 is a diagram illustrating the positioning of the vanes of FIG. 3in one direction to produce a lateral force in one direction.

FIG. 5 is a diagram illustrating the positioning of the vanes of FIG. 3to produce a lateral force in the opposite direction.

FIG. 6 illustrates a modification in the construction of the vaneswherein each of the vanes is split into two halves, each half of all thevanes being separately pivotal from the other half of all the vanes toproduce a rotary moment force about the duct longitudinal axis;

FIG. 7 is a diagram illustrating the construction of one of the vanesand the manner for pivoting it;

FIG. 8 illustrates an alternative construction of one of the vanes andthe manner for pivoting it;

FIG. 9 illustrates one arrangement that may be used for providing twocascades or assemblies of vanes at the inlet end of the duct of FIG. 9;

FIG. 10 illustrates another arrangement that may be used for providingtwo cascades or assemblies of vanes at the inlet end of the duct;

FIG. 11 illustrates a VTOL aircraft vehicle including a single ductedfan for propulsion and control purposes;

FIG. 12 is a view similar to that of FIG. 3 but illustrating theprovision of a cascade or plurality of vanes also at the exit end of theduct;

FIGS. 13 a-13 d illustrate various pivotal positions of the two cascadesof vanes in the ducted fan of FIG. 12, and the forces produced by eachsuch positioning of the vanes;

FIG. 14 is a top view diagrammatically illustrating another constructionwherein the vanes extending across the inlet of the duct are dividedinto two groups together producing the desired net horizontal controlforce;

FIGS. 15 a and 15 b diagrammatically illustrate the manner in which thedesired net horizontal control force is produced by the vanes of FIG.14; and

FIG. 16 is a view corresponding to that of FIG. 14 but illustrating avariation in the vane arrangement for producing the desired nethorizontal control force.

DESCRIPTION OF PREFERRED EMBODIMENTS

The vehicle illustrated in FIG. 1, and therein generally designated 2,is a VTOL aircraft including a frame or fuselage 3 carrying a ducted fanpropulsion unit 4 at the front, and another similar propulsion unit 5 atthe rear. The vehicle payload is shown at 6 and 7, respectively, onopposite sides of the fuselage, and the landing gear as shown at 8.

FIGS. 2 and 3 more particularly illustrate the structure of propulsionunit 4, which is the same as propulsion unit 5. Such a propulsion unitincludes a duct 10 carried by the fuselage 3 with the vertical axis 10 aof the duct parallel to the vertical axis of the vehicle. Propeller 11is rotatably mounted within the duct 10 about the longitudinal axis 10 aof the duct. Nose 12 of the propeller faces upwardly, so that the upperend 13 of the duct constitutes the air inlet end, and the lower end 14of the duct constitutes the exit end. As shown particularly in FIG. 3,the upper air inlet end 13 is formed with a funnel-shaped mouth toproduce a smooth inflow of air into the duct 10, which air is dischargedat high velocity through the exit end 14 of the duct for creating anupward lift force.

To provide directional control, the duct 10 is provided with a pluralityof parallel, spaced vanes 15 pivotally mounted to, and across, the inletend 13 of the duct. Each of the vanes 15 is pivotal about an axis 16perpendicular to the longitudinal axis 10 a of the duct 10 andsubstantially parallel to the longitudinal axis of the vehicle frame 2,to produce a desired horizontal control force in addition to the liftforce applied to the vehicle by the movement of air produced by thepropeller 11. Thus, as shown in FIG. 4, if the vanes 15 are pivoted inone direction about their respective axes, they produce a desiredcontrol force in the direction of the arrow F1 in FIG. 4; and if theyare pivoted in the opposite direction, they produce a desired controlforce in the direction of the arrow F2 in FIG. 5. As shown in FIG. 3(also FIGS. 7, 8, 12), the vanes 15 are of a symmetric airfoil shape andare spaced from each other a distance approximately equal to the chordlength of the vanes.

FIG. 6 illustrates a variation wherein each of the vanes 15, instead ofbeing pivotally mounted as a unit for its complete length to produce thedesired side control force is split into two half-sections, as shown at15 a and 15 b in FIG. 6, with each half-section separately pivotal fromthe other half-section. Thus, all the half-sections 15 a may be pivotedas a unit in one direction as shown by arrow D₁, and all thehalf-sections 15 b may be pivoted in the opposite direction as shown byarrow D₂, to thereby produce any desired side force or rotary moment inaddition to the lift force applied to the vehicle by the propeller.

As shown in FIG. 7, each of the vanes 15 is pivotally mounted about axis16 passing through a mid portion of the vane. FIG. 8 illustrates amodification wherein each vane includes a fixed section 17, whichconstitutes the main part of the vane, and a pivotal section or flap 18pivotally mounted at 19 to the trailing side of the fixed section. Itwill thus be seen that the pivotal section or flap 18 may be pivoted toany desired position in order to produce the desired control force inaddition to the lift.

FIG. 9 illustrates a variation wherein the ducted fan (4 and/or 5FIG. 1) includes a second plurality or cascade of parallel, spacedvanes, one of which is shown at 20, pivotally mounted to and across theinlet end 13 of the duct 10. Thus, each of the vanes 20 of the secondplurality is closely spaced to the vanes 15 and is pivotal about an axisperpendicular to the pivotal axis of the vanes 15, as well as to thelongitudinal axis 10 a of the duct.

In the variation illustrated in FIG. 9, the two cascades of vanes 15,20, are arranged in parallel, spaced planes. FIG. 10 illustrates avariation wherein the two cascades of vanes at the inlet end of the ductare intermeshed. For this purpose, each of the vanes 21 of the secondplurality would be interrupted so as to accommodate the crossing vanes15 of the first plurality, as shown in FIG. 10. Another possiblearrangement would be to have the vanes of both cascades interrupted forpurposes of intermeshing.

FIG. 11 illustrates a VTOL aircraft vehicle, therein generallydesignated 22, including a single ducted fan 24 carried centrally of itsfuselage 23. Such a vehicle could include the arrangement of vanesillustrated in either FIG. 9 or in FIG. 10 to provide the desiredcontrol forces and moments in addition to the lift forces. In such avehicle, the payload may be on opposite sides of the central ducted fan24, as shown at 25 and 26 in FIG. 11. The vehicle may also include otheraerodynamic surfaces, such as rudders 27, 28 to provide steering andother controls.

FIG. 12 illustrates a further embodiment that may be included in eitherof the vehicles of FIGS. 1 and 11 wherein the duct 10 also has a secondplurality or cascade of parallel, spaced vanes, but in this case, thesecond plurality are pivotally mounted to and across the exit end 14 ofthe duct 10. Thus, as shown in FIG. 12, the duct 10 includes the firstplurality or cascade of blades 15 mounted to and across the inlet end 13of the duct, and a second plurality or cascade of blades 35 mounted toand across the exit end 14 of the duct 10, also perpendicular to thelongitudinal axis of the duct and substantially parallel to thelongitudinal axis of the vehicle frame. Each assembly or cascade 15, 35of the vanes may be pivoted independently of the other to produceselected side forces or rotary moments about the duct's transverse axis10 b for pitch or roll control of the vehicle.

This is more clearly shown in the diagrams of FIGS. 13 a-13 d. Thus,when the two cascades of vanes 15, 35, are pivoted in oppositedirections, they produce a rotary moment about the transverse axis 10 bof the duct 10 in one direction (e.g., counter-clockwise as shown inFIG. 13 a); when they are pivoted in the same direction, they produce aside force in one direction (e.g. left) as shown in FIG. 13 b whenpivoted in opposite directions but opposite to the arrangement shown inFIG. 13 a, they produce a rotary moment in the opposite clockwisedirection as shown in FIG. 13 c; and when they are pivoted in the samedirection but opposite to that shown in FIG. 13 b, they produce a sideforce in the opposite (e.g. right) direction, as shown in FIG. 13 d.

FIG. 14 is a top view illustrating another construction of ducted fanpropulsion unit, generally designated 20, including a duct 22 having aplurality of vanes 24 extending across the inlet end of the duct. Inthis case, the vanes 24 are divided into a first group of parallel vanes24 a extending across one-half the inlet end of the duct 22, and asecond group of parallel vanes 24 b extending across the remaining halfof the inlet end of the duct.

FIG. 14 also illustrates the nose 26 of the propeller within the duct22. The propeller is rotatably mounted within the duct 22 about thelongitudinal axis of the duct, with the nose 26 of the propellercentrally located at the air inlet end of the duct such that the airdischarged at a high velocity through the opposite end of the ductcreates an upward lift force.

As shown in FIG. 14, the first group of parallel vanes 24 a extendingacross one half of the inlet end of the duct 22 are pivotal about axes25 a at a predetermined acute angle a with respect to the longitudinalaxis 20 a of the vehicle frame and thereby of the direction of movementof the vehicle as shown by arrow 27; and that the second group ofparallel vanes extending across the remaining half of the inlet end ofthe duct are pivotal about axes 25 b at the same predetermined angle a,but in the opposite direction, with respect to the longitudinal axis 20a of the vehicle frame. The two groups of vanes 24 a, 24 b areselectively pivotal to produce a desired net horizontal control force inaddition to the lift force applied to the vehicle.

The foregoing operations are illustrated in the diagrams of FIGS. 15 aand 15 b. Both FIG. 15 a and 15 b illustrate the control forcesgenerated when the vehicle includes two ducted fan propulsion units 20,30, at the opposite ends of the vehicle and coaxial with the vehiclelongitudinal axis 20 a. It will be appreciated that comparable forcesare produced when the vehicle is equipped with only one ducted fanpropulsion unit shown in FIG. 14.

FIG. 15 a illustrates the condition wherein the two groups of vanes 24a, 24 b are pivoted to equal angles about their respective axes. Thevanes thus produce, in addition to the lift force, control forces ofequal magnitude and angles on opposite sides of the vehicle longitudinalaxis 20 a, so as to produce a net force, shown at Fa, coaxial with thevehicle longitudinal axis 20 a.

The two groups of vanes 34 a, 34 b of the rear propulsion unit 30 arepivotal in the same manner about their respective pivotal axes andthereby produce a net force Fa also coaxial with the vehiclelongitudinal axis 20 a.

FIG. 15 b illustrates a condition wherein the two groups of vanes 24 a,24 b in the fore propulsion unit 20, and the two groups of vanes 34 a,34 b in the aft propulsion unit 30, are pivoted about their respectiveaxes to unequal angles, thereby producing net side forces Fb at an angleto the vehicle longitudinal axis 20 a. Thus, by controlling the pivotangles of the vanes 24 a, 24 b and 34 a, 34 b about their respectivepivotal axes, a net control force may be generated as desired in theplane of the vanes.

FIG. 16 illustrates a ducted fan propulsion unit, generally designated40, also including two groups of vanes 44 a, 44 b, extending acrossone-half of the inlet of the duct 42 and pivotally mounted about axes 45a, 45 b at a predetermined angle, (e.g., 45°) to the longitudinal axis40 a of the vehicle. In this case, however, the vanes 44 a, 44 b areoriented in the forward direction, rather than in the aft direction asin FIG. 14, but the operation, and the forces generated by the vanes,are basically the same as described above with respect to FIGS. 14, 15a, 15 b.

It will be appreciated that any of the foregoing arrangements of FIGS.14-16, as well as those of FIGS. 1-11, could also be provided at theexit ends of the ducts, as shown in FIGS. 12-13 d, to produce thedesired control forces in addition to the lift forces. The vanes are notintended to block air flow, but merely to deflect air flow to producethe desired control forces. Accordingly, in most applications the vaneswould be designed to be pivotal no more than 15° in either direction,which is the typical maximum angle attainable before flow separation.

Since the control forces and moments are generated by horizontalcomponents of the lift forces on the vanes themselves, the vanes shouldpreferably be placed on the intake side of the propeller as far from thecenter of gravity of the vehicle as possible for creating the largestattainable moments. The same applies if vanes are provided on the exitside of the ducts.

While the invention has been described above particularly with respectto air vehicles, it will be appreciated that the invention, or variousaspects of the invention as described above, can also be advantageouslyused with other types of vehicles such as sea vehicles, to providepropulsion and directional control to the vehicle.

Accordingly, while the invention has been described with respect toseveral preferred embodiments, it will be understood that these are setforth merely for purposes of example, and that many other variations,modifications and applications of the invention may be made.

1-22. (canceled)
 23. A vehicle, comprising: a vehicle frame; a ductcarried by said vehicle frame with the longitudinal axis of the ductperpendicular to the longitudinal axis of the vehicle frame; a propellerrotatably mounted within said duct about the longitudinal axis of theduct to force an ambient fluid therethrough from its inlet at the upperend of the duct through its exit at the lower end of the duct, andthereby to produce an upward lift force applied to the vehicle; and aplurality of parallel, spaced vanes pivotally mounted to and across theinlet end of the duct about pivotal axes perpendicular to saidlongitudinal axis of the duct and substantially parallel to saidlongitudinal axis of the vehicle frame, said vanes being selectivelypivotal about their axes to produce a desired horizontal force componentto the lift force applied to the vehicle, wherein said vanes include: afirst group of parallel vanes extending across one half of the inlet ofsaid duct and pivotal about axes at a predetermined acute angle withrespect to the longitudinal axis of the vehicle frame; and a secondgroup of parallel vanes extending across the remaining half of the inletend of said duct and pivotal about axes at said predetermined angle, butin the opposite direction, with respect to the longitudinal axis of thevehicle frame, wherein said first and second groups of vanes beingselectively pivotal to produce a desired net control force in additionto the lift force applied to the vehicle.
 24. The vehicle according toclaim 23, wherein said predetermined angle is 45 degrees.